Method of setting an electron-projecting apparatus to uniformly heat a coated metal base



United States Patent O 3,441,709 METHOD OF SETTING AN ELECTRON-PROJECT- ING APPARATUS TO UNIFORMLY HEAT A COATED METAL BASE Anthony P. Martocci, Bethlehem, Pa., assignor to Bethlehem Steel Corporation, a corporation of Delaware Filed Apr. 18, 1968, Ser. No. 722,296 Int. Cl. B23k 9/00 U.S. Cl. 219-121 7 Claims ABSTRACT OF THE DISCLOSURE A method of setting an apparatus projecting one or more moving electron beams onto a metallic coated metal base such that the coated surface is uniformly heated. The apparatus is adjusted until the coated surface is at the lowest temperature at which a substantially uniform color of an alloy composed of the coating and base occurs over the coated surface. The color of this alloy is different than the color of the coating itself, and the occurrence of the alloys color indicates temperature uniformity over the coated surface.

Background of the invention During the process of coating a metal article by depositing metallic vapors upon it in a vacuum chamber, the article may be heated both bef-ore and after the coating operation. Where the article isa strip moving through the vacuum chamber, it may be heated by one or more electron beams oscillating across the strips width. Where a plurali-ty of oscillating beams are used they may impinge upon the stri-p in a line across its width, with each oscillating across a. portion of this line.

Apparatus projecting these beams contain controls for regulating the intensity of the beams, Icontrols for regulating the oscillation frequency of the beams, controls for regulating .the length of sweep each beam oscillates across, and controls for positioning the center of this sweep, However, difficulties have been encountered in setting the apparatus such that the strip is uniformly heated.

Obviously, a single oscillating beam sweeping across only -a part of the strips width cannot uniformly heat the strip. Where a plurality of electron beams are used, the length of their sweeps may be even more critical. If the sweeps of adjacent beams overlap, or if a substantial gap i-s left between them, a uniform temperature cannot be obtained across the strip.

Of course where a plurality of beam-s oscillating across equal portions of the strips width are used, they must be of the salme inten-sity to uniformly heat the width.

A beam having a too low oscillation frequency will overheat a moving str-ip at those loc-ations where it changes direction, i.e., at the ends of its sweep. At these points the beam will impinge upon the strip effectively twice and cause localized overheating. However, by increasing the beams oscillation frequency the distribution of heat across the strips width may be equalized.

A further situation requiring adjustment occurs when the center of that portion of the strips width being heated by a beam does not coincide with the center of the beams sweep. This situation may be corrected by aligning the sweeps center with the center of the portion being heated. This adjustment has been found satisfactory for deposition coating purposes.

A previously -used Imethod of overcoming these problems set the apparatus 'by initially heating an uncoated steel strip with the electron beams. The apparatus was lCe adjusted until a substantially uniform reddish glow of the steel occurred across the strips width. With the apparatus thus set, the electron beams could be used to hea-t either a coated or uncoated strip as required. However, this methods accuracy was limited to differences in temperature of 10G-200 F, across the strips width.

Summary of the invention According to the invention, an apparatus projecting one or more moving electron beams onto a metallic coated metal base is set to uniformly heat at least a portion of the coated surface by adjusting the apparatus until that portion of the coated surface is at the lowest temperature at which a substantially uniform color of an alloy, composed of the coating and base, occurs over the portion. The color of the alloy must be different .than the color of the coat-ing itself, and the occurrence of the alloys color ind-icates a temperature uniformity .to within 25-50" F. over that portion of the coated surface being uniformly heated Brie)c description of the drawings FIGURE l is a schematic view showing apparatus projecting `a single oscillating electron beam onto a moving metal strip.

FIGURE 2 is similar to FIGURE 1 but shows two oscillating electron beams being projected onto a moving metal strip.

Description of the preferred embodiment FIGURES 1 and 2 show a metal strip S being passed under apparatus projecting one or more electron beams B onto the -strips upper surface. The `strip is composed of a metal base having at least one metallic coated surface. The coating is substantially uniformly distributed over this surface and of a different color than an alloy composed of the coating and base which will be produced when the coated surface of the strip is heated by the electron beams. A satisfactory example would be a bright aluminum coating which diffuses into a steel base, thereby yielding a uniform dull gray alloy coating. Zinc would also be a satisfactory coating for a steel base. The coating need not be on the surface of the strip upon which the beam or beams impinge. Should the underside of strip S shown in FIGURES l and 2 be coated, this surface will be heated indirectly by the electron beams B since heat will be conducted through the strip.

For each electron beam being projected in FIGURES 1 and 2, the apparatus has an electron emissive filament 1 having a suitable current supply and control 2, two accelerating electrodes 3a and 3b having a suitable voltage supply 4; focusing coils 5 having a suitable control 6; and deflection coils 7, also having a suitable control 8. Electron beam B is emitted from electron emissive lament 1 which is raised to an electron emission temperature by a current supplied and controlled by filament supply and control 2, which thereby controls the beams intensity. The beam then passes between two accelerating electrodes, 3a and 3b, which are maintained at a positive potential with respect to filament 1 by accelerating voltage supply 4. Each beam is then passed through focusing coils 5 and deflection coils 7. At the deection coils the beam is caused to oscillate across at least a portion of the strips width along line A. In addition, any necessary changes in the length of the beams sweep, in the center of this sweep, and in the beams oscillation frequency are effected at this point.

As strip S moves under the apparatus its coated surface is heated by the electron beam or Vbeams B. To set the apparatus such that the strip is uniformly heated across its width, the apparatus is adjusted until a section across the strips width is at the lowest temperature at which the color of the alloy occurs substantially uniformly across this section.

This color need not occur at that section of the strip upon which the beam or beams impinge, i.e., along line A, 'but may occur across a section adjacent and parallel to the impinged section. This adjacent section will be heated by conduction along the length of the strip. Since the two sections are parallel they will both be of a uniform temperature, although not of the same temperature, when the color of the alloy occurs across the adjacent section. If the electron-projecting apparatus is be used to be used to uniformly heat an uncoated strip, the apparatus may be set by adjusting it to uniformly heat a coated strip prior to its use with the uncoated strip.

I claim:

1. A method of setting an apparatus projecting at least one electron beam onto a metal base having a metallic coated surface, such that said beams substantially uniformly heat at least a portion of the coated surface; said beams moving with respect to said coated base, said coating being substantially uniform and of a different color than an alloy composed of said coating and base produced when said beams heat the coated surface, said method comprising: adjusting said apparatus to heat at least a portion of the coated surface to the lowest temperature at which the color of said alloy occurs substantially uniformly over said portion.

2. The method as recited in claim 1 wherein:

said metallic coated metal base is in the form of a strip;

one electron beam oscillates substantially across the width and impinges upon the coated surface of said strip;

and the coated surface of said strip is heated to the lowest temperature at which the 4color of said alloy occurs substantially uniformly across its width.

3. The method as recited in claim 2 wherein said strip is moving in the direction of its length.

4. The method as recited in claim 3 wherein adjusting said apparatus effects any necessary changes in the length of sweep of oscillation, the center of the sweep of oscillation, and oscillation frequency of the beam.

5. The method as recited in claim 1 wherein:

said metallic coated metal base is in the form of a Strip;

a plurality of electron beams impinge upon the coated surface of said strip in a line across the width of said strip, with each of said beams oscillating over a portion of this line;

and the coated surface of said strip is heated to the lowest temperature at which the color of said alloy occurs substantitally uniformly across its width.

6. The method as recited in claim 5 wherein said strip is moving in the direction of its length.

7. The method as recited in claim 6 wherein adjusting said apparatus effects any necessary changes in the length of sweep of oscillation, the center of the sweep of oscillation, oscillation frequency, and intensity of each of the beams.

References Cited UNITED STATES PATENTS 1,630,485 5/1927 Gerdts 73-358 2,928,791 3/1960 Loconti 73-356 3,210,518 10/1965 Morley et al 219--121 3,325,620 6/1967 Hunt et al. 219--50 OTHER REFERENCES News Bureau, General Electric Company, Schenec tady, N.Y. January 1946.

JOSEPH V. TRUHE, Primary Examiner.

US. Cl. X.R. 

